A fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte. A fuel, e.g. hydrogen, an alcohol such as methanol or ethanol, or a hydride, is supplied to the anode and an oxidant, e.g. oxygen or air, is supplied to the cathode. Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat. Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.
Electrocatalysts for fuel oxidation and oxygen reduction are typically based on platinum or platinum alloyed with one or more other metals. The platinum alloy can be used as a high surface area metal black (an unsupported catalyst) or can be deposited onto a conductive carbon substrate (a supported catalyst).
Platinum is an expensive metal, so it is desirable to decrease the proportion of platinum in the electrocatalyst whilst maintaining or improving catalytic activity. The present inventors have sought to provide improved platinum catalysts having similar or improved activity to known catalysts but having a lower platinum content.